Provide possibility to pass packages and search paths for packages as parameters.

fpkg.pas:
  + new unit which contains the base types related to package files (most importantly "tpackage")
globals.pas:
  + new variable "packagesearchpath" which contains all paths in which package files should be looked for
  + new variable "packagelist" which contains a list of all packages that should be used in a program or library
  * InitGlobals & DoneGlobals: initialize/finalize "packagesearchpath" accordingly ("packagelist" is handled in unit fpkg using a init/done-callback)
options.pas:
  + TOption: new fields "parapackagepath" and "parapackages" to keep track of package search paths and package files passed as parameters
  * TOption.interpret_option: use '-Fp' for package search paths and '-FP' for package files
  * read_arguments: apply the passed package search paths and packages to their respective containers

git-svn-id: http://svn.freepascal.org/svn/fpc/branches/svenbarth@28796 3ad0048d-3df7-0310-abae-a5850022a9f2